Observations on the Control of Stepping and Hopping Movements in Man,
MCGILL UNIV MONTREAL (QUEBEC) DRB AVIATION MEDICAL RESEARCH UNIT
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The presence of a form of stretch reflex, previously described in the arm by other authors, has been confirmed in the gastrocnemius muscle of the human leg. The electromyographic e.m.g. manifestation of this reflex occurred 120 msec following a sharply applied, and maintained, dorsiflexing force to the foot. This form of response is referred to in this article as the functional stretch reflex FSR. To determine the contribution of the FSR to the control of normal leg movement, the e.m.g. activity in the above muscle was monitored during single downward steps of 12.7, 25.4 and 38.1 cm and during repetitive, rhythmic, hopping movements on one foot. It was found that e.m.g. activity associated with steps to the ground began 141 msec after contact, when the e.m.g. usually became temporarily inactive. It is inferred from these results that the muscular deceleration associated with landing was brought about by the release of a preprogrammed pattern of neuromuscular activity which was inaccessible to reflex activity resulting from the mechanical event of landing, rather than by a stretch reflex.
- Anatomy and Physiology